In the paid search industry, advertisements which are considered candidates for display in response to search query terms are typically determined based upon advertisers placing bids on keywords. Advertisers can select among several search query term match types including exact match, phrase match, and broad match. Exact match determines that an advertisement should be selected for display if a search query term is identical to the keyword bid upon by the advertiser. Phrase match determines that an advertisement should be selected for display as long as the bid upon keyword is contained as a phrase somewhere within the search query term. Broad match determines that an advertisement should be selected for display as long as all of the individual terms included in the bid upon keyword are contained somewhere within the search query term.
Keyword-based matching techniques have a number of drawbacks. In particular, management is often too complicated and/or costly for many small to medium-sized advertisers. For instance, to successfully employ a keyword-based matching technique, an advertiser must perform research into user search queries to determine which query terms are commonly searched upon and, based on this information, decide which keywords to bid upon. Subsequently, they must decide how much to bid on each keyword and if they desire to place different bids, or different types of bids, on different keywords. As the keyword bid landscape changes frequently, the advertiser must also constantly monitor their position on the keywords they have bid upon to ensure their advertisements are being displayed to enough users to justify their expense on an on-going basis.
Additionally, the search query term tail presents an issue in keyword-based matching techniques. There are many search terms with very little traffic which, in aggregate, are valuable but are difficult to manage due to their great numbers and low traffic volumes. This is the search query term tail. With keyword-based matching, an advertiser placing phrase and broad match bids on keywords may cover a portion of the search query term tail. When this occurs, it tends to result in the advertisements being displayed, in part, on search query terms for which they are not relevant. Such low relevance matches create user dissatisfaction with the search engine displaying the advertisements as well as challenges for an advertising system attempting to optimize revenue for that search engine.